Nasty rot

Photo competition: Special prize ‘saprotrophic organisms’

In addition to other, undetermined infections, the picture shows fruit rot (Monilia fructigena) around the calyx of an apple that was left in the photographer’s garden for a few days. Fruit rot is caused by a pathogenic fungal infection on pome and stone fruit such as apples, pears, cherries and plums. Starting from an injury to the fruit skin as an entry point for fungal spores, e.g. through a hole drilled by insects, a brown, rotting spot first appears, which rapidly enlarges. Soon, circular pads of spores form on it, hence the name ‘cushion mildew’. The fungus survives the winter on dried fruit mummies that remain on the tree or on fallen fruit and infected shoots. To combat the disease, possible sources of infection must be reduced, for example by trimming back infected shoots.